You know what, JEB20005 and nascarbebe, you both mentioned shopping in your posts and BH's... I'm very seriously convinced that has something to do with it.
Here's my reasoning, it may sound a little nuts, but I think it's worth considering. TMI begins: Both DP and I get the severe urge to poop when out somewhere shopping that has alot of plastic (blockbuster, for example tends to set either of us off, even sans pregnancy). I've noticed the past two weeks that I can't be in any store (grocery, target, blockbuster) for a few minutes without that plastic hitting me, I think I'm more sensitive. (Maybe most pregnant women are?) Then I'm overwhelmed by an intense urge to go and BH's for as long as I'm in that store (and I haven't really had any BH's to speak of besides this). My theory is that the plastic fumes work like castor oil, or any other agent that gets those lower gut/pelvic floor muscles a-squeezing. I wouldn't be surprised if your being out and shopping had some effect on your contractions as well. I have no idea if there have been any studies on this, but considering my own non-pregnant and Mr Toona's reactions to plastics, I wouldn't call it too far fetched to extrapolate extra ctx's from it.
In fact I told Mr Toona yesterday after shopping, that if for some reason my labor stalls, we'll just go to Target and walk around a while, that should kick it back into gear. Forget Castor Oil, and forget Pitocin, that stuff seems to do the trick!
Not sure about the labor-like contractions, but if you're concerned about pre-term labor, maybe steer clear of plastics for awhile? I was considering limited shopping myself... Not that I'm worried about pre-term, but I"d hate to jar anything, KWIM?